1. Field of the Invention
The present invention relates to a thermosensible flow sensor for measuring, for example, the intake air flow of an internal combustion engine and, more particularly, to a flow detector element of a thermosensible flow sensor for measuring the flow velocity or the flow rate of fluid on the basis of heat transfer phenomenon from a heat generator or a part heated by the heat generator to the fluid.
2. Description of the Related Art
A conventional thermosensible flow sensor is the one in which there are provided on a substrate a heat resistor and a fluid temperature-measuring resistor, and a cavity that is formed by removing partially the substrate is located under the heat resistor, as disclosed in the Japanese Patent Publication No. 3455473.
Furthermore, another conventional thermosensible flow sensor is the one in which there are provided on a substrate a heat resistor and a fluid temperature-measuring resistor, and cavities are formed individually under each of these heat resistor and fluid temperature-measuring resistor, as disclosed in the Japanese Patent Publication (unexamined) No. 249693/1994.
In the case where a thermosensible flow sensor as described above is mounted onto an automobile to make an engine control, there are some cases in which a throttle is fully open to make a quick start from in the state that an idle operation state continues under at a constant temperature, and then the temperature in an engine room is sufficiently raised.
In this case, under the idle operation, the engine room is at high temperature, and in a thermosensible flow sensor mounted in the engine room, the temperature of an air current flowing through the thermosensible flow sensor section, and the temperature of an element support portion of the thermosensible flow sensor are both in a high-temperature state. When a quick start and a quick acceleration are made at such time, although the engine room is still remained at high temperature, an air current flowing through the thermosensible flow sensor and the element support portion will be cooled.
In this respect, in the above-mentioned Japanese Patent Publication No. 3455473, a heat resistor and a fluid temperature-measuring resistor are formed on a substrate, and a cavity is formed under the heat resistor alone. Therefore, the heat capacity at the fluid temperature-measuring resistor section becomes larger, thus thermal response delays occur with respect to the change of temperatures of an air current at the fluid temperature-measuring resistor, and fluid temperature detection error occurs, eventually resulting in the occurrence of error in detection values of flow rates.
Moreover, in the above-mentioned Japanese Patent Publication (unexamined) No. 249693/1994, a cavity is formed also under the fluid temperature-measuring resistor as is under the heat resistor, so that even if the temperature of fluid is varied, it is possible to reduce detection error at the fluid temperature-measuring resistor. However, a problem exists in that the thermal response at the fluid temperature-measuring resistor is too early.
That is, the heat capacity at an element support portion is large, so that thermal response delays will occur at the element support portion, and thus off-balance will occur between the thermal response of the fluid temperature-measuring resistor and the thermal response of the element support portion. As a result, a problem exists in the occurrence of error of detection values of flow rates.